The present invention relates to preparation of perhaloalkanoyl chloride by contacting 1,1,1-trichloroperhaloalkanes with a SO.sub.3 -containing substance in the presence of a catalytic amount of a halogen catalyst, such as bromine.
Perhalo compounds wherein the halogen is chlorine or fluorine are particularly resistant to oxidizing agents. Specifically, trifluoroacetyl chloride, CF.sub.3 COCl, a known chemical compound having a boiling point of -19.degree. C., is a valuable chemical intermediate, useful for the preparation of trifluoroethanol, trifluoroacetic acid, and trifluoroacetaldehyde. Trifluoroethanol, further is a raw material useful in the manufacture of novel anesthetic compounds. Perhaloalkanoic acids, such as trifluoroacetic acid is also an intermediate for the preparation of compounds useful as herbicides, insecticides, dyes, etc. Higher homologous perhaloalkanoyl chlorides, for example perfluorooctanoyl chloride, CF.sub.3 (CF.sub.2).sub.6 COCl is easily converted to the carboxylic acid or acid salt which is useful as a surfactant.
In the relevant prior art procedures, trifluoroacetyl chloride has been prepared by the catalytic hydrolysis of 1,1,1-trifluoro-2,2,2-trichloroethane, using oleum, (sulfur trioxide dissolved in sulfuric acid), in the presence of toxic mercurial salt catalysts. These prior art procedures are described, particularly in Lawlor and Braid; U.S. Pat. No. 3,102,139; Dittman and Zager: U.S. Pat. No. 3,160,659; and Pauchsch et al.: U.S. Pat. No. 3,725,475.
Trifluoroacetyl chloride has also been previously prepared by subjecting a mixture of chlorine, oxygen and 1,1,1-trifluoro-2,2,2-trichloroethane to ultraviolet irradiation under anhydrous conditions, as described by Braid and Lawlor in U.S. Pat. No. 3,151,051.
In general, methods described in the prior art for the preparation of perhaloalkanoyl compounds have required excessively prolonged reaction times, elevated reaction pressures, hazardous ultraviolet radiation, and have generally resulted only in low yields of the desired end products, frequently accompanied by losses of starting materials due to side reactions such as carbon-to-carbon bond cleavage. In addition, the prior art preparations discussed above have also been characterized by the need to use toxic mercurial salt catalysts, which require costly environmental pollution control systems, and which create difficult environmental waste disposal problems, particularly associated with the safe disposal of by-product sulfuryl chloride-containing mercurial salts.
Thus, a process for the preparation of perhaloalkanoyl chloride from 1,1,1-trichloroperhaloalkane using a nonmetallic, nonpolluting, and low cost halogen catalyst, has significant commercial and technical value.
Accordingly it is an object of the present invention to provide a process for the preparation of perhaloalkanoyl chloride in the presence of a halogen catalyst which is non-metallic and which embodies none of the operating and environmental disadvantages of the prior art procedures.